Treating metal with a cleaning agent in a combustible solvent before coating

ABSTRACT

A process of cleaning a metal in the form of wires, rods, tubes, flat sheets and coiled sheets is provided in which the metal is brought into contact with a flame produced by the combustion of a gaseous fuel under superatmospheric pressure in the presence of a metal cleaning additive dissolved in a combustible solvent.

United States Patent 1191 Miller 1 1 Dec. 2, 1975 [54] TREATING METAL WITH A CLEANING 3,052,014 9/1962 Falcon 134/15 X AGENT IN A COMBUSTIBLE SOLVENT 3.741.792 6/1973 Peck et al. [17/46 FC BEFORE COATING FOREIGN PATENTS OR APPLICATIONS Inventor: Russell 0 Miller, C g 629.926 9/1949 United Kingdom..-. 134/19 [73] Assignee: J. M. Eltzroth & Associates, Inc.,

Schaumburg, Ill. Primary E.\'aminerS. Leon Bashore Assistant Examiner-Richard V. Fisher [22] Flled' 1973 Attorney, Agent, or Firm-Johnston. Keil, Thompson [21] Appl. N0.: 417,259 & Shurtleff [52] U.S. Cl. 427/327; 134/14; 134/15; 57 ABSTRACT 134/19; 134/41; 427/444 51 1m. 01. c231" 17/00; B08B 7/00 A Process of cleamng metal of [581 Field of Search 134/14 15, 19, 35 rods, tubes, flat sheets and coiled sheets is provided in 34/41. 117/4 c 49. 27 318 7 444 which the metal 15 brought 111110 contact With a flame i produced by the combustion of a gaseous fuel under [56] References Cited superatmospheric pressure in the presence of a metal UNITED STATES PATENTS cleaning additive dissolved in a combustible solvent. 2,288,980 7/1942 Turin 134/15 X 6 Claims, N0 Drawings I TREATING METAL WITH A CLEANING AGENT IN A COMBUSTIBLE SOLVENT BEFORE COATING BACKGROUND It is well known that ferrous and non-ferrous metals in the form of wires, rods, tubes, flat sheets, and coiled sheets normally have to be cleaned before protective coatings can be applied thereto. Conventional cleaning baths involve the use of alkalis and surfactants, hot solvent degreasers, and acid (phosphate) and surfactants.

For some time there has been a need for a process for cleaning and coating metal of the type described wherein the conventional alkali and acid-type cleaning methods and solvent cleaning methods are replaced with methods that do not involve the disposal of large amounts of solvents or waste waters containing sub stances which are harmful to the environment.

OBJ ECTS One of the objects of the present invention is to provide a cleaning and coating process which is particularly applicable to the cleaning and the application of protective coatings to wire, rods, tubes, flat sheets and coiled sheets, wherein conventional cleaning processes are replaced with a process utilizing a flame in direct contact with the metal containing a metal cleaning additive which flame containing said additive is applied to the metal at controlled metal temperatures.

Another object of the invention is to provide a new and improved coating process in which the surface of a metal of the type described is prepared or conditioned so that a better surface is formed which is adapted to receive a protective coating and the protective coating adheres thereto, all in a relatively simple process which does not require disposal or recycling of waste waters and does not cause any harm to the environment.

A further object of the invention is to provide a new and improved process of the type described in which cleaning agents and other additives including protective coating materials are applied to metals of the type described either sequentially or simultaneously by means of a flame which is brought into direct contact with the metal. Other objects will appear hereinafter.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention a ferrous or nonferrous metal in the form of wires, rods, tubes, flat sheets and coiled sheets is brought into contact with a flame produced by the combustion of a gaseous fuel under superatmospheric pressure in the presence of a metal cleaning agent dissolved in a combustible solvent at controlled temperatures and for periods of time sufficient to clean said metal and provide a surface adapted to receive a protective coating without destroying the physical properties of the metal.

DETAILED DESCRIPTION OF THE INVENTION The exact manner in which the present invention is practiced will depend to some extent upon the type of metal which is processed in accordance with the invention. In general, the invention is applicable to wire, rods, tubes, flat sheets and coiled sheets made from ferrous metals such as iron andsteel, or non-ferrous metals such as aluminum and aluminum alloys, copper and copper alloys, aluminized and galvanized iron and steel where the surfaces are of aluminum or zinc, and other 2 types of metals which can be subjected to flame treatment without destroying the physical properties.

The gaseous fuel which is used to produce the flame can be acetylene, natural gas, methane, ethane, propane, butane, or other fuel in gaseous form. The fuel is normally anhydrous and is maintained under supcratmospheric pressures. If the fuel does not contain oxygen. oxygen must be supplied either as such or in the form of air either prior to or at the point of combustion.

The metal cleaning agent which is dissolved in a combustible solvent is entrained in the gaseous fuel or applied to the metal prior to combustion. This can be accomplished by bubbling the gaseous fuel through a solution of the cleaning agent in the combustible solvent, or by mechanical application of the cleaning agent in a combustible solvent before the metal reaches the flame area, or by injecting the cleaning agent into the fuel stream. A preferred metal cleaning agent dissolved in the combustible solvent is a solution of anhydrous syn thetic methanol saturated with boric acid.

Instead of methanol, other combustible solvents can be employed, for example, isopropanol, hexanol, glycerol, ethylene glycol. diethylene glycol, ethyl acetate. acetone, glycerol, acetic acid. ethyl alcohol, N-

solvents with or without small amounts of water which may be present in some of the solvents are all capable.

of dissolving boric acid to some extent in amounts varying from 0.6 percent for acetone at 20 to 30C. to a much larger extent in the case of methanol. These same solvents can be used to produce solutions of other additives which can be appliedto the aforesaid metals entraining the solutions in the gaseous fuel and bringing the metal into contact with a flame produced by the combustion of the gaseous fuel containing the entrained additive.

Examples of such other additives are phosphoric acid and related acids and salts, acetic acid and related acids and salts, sulfuric acid and related acids and salts, ox-

alic, citric, tartaric and other similar acids and salts, trivalent chromium compounds and zirconium, aluminum, magnesium, iron and, zinc compounds which are soluble or dispersible in said solvents.

A preferred procedure is to bubble a gaseous fuel such as acetylene which is normally maintained under superatmospheric pressure in a cylinder or other storage container through a solution of the cleaning agent, e.g., boric acid, dissolved in the combustible solvent,

e.g., methanol, to produce a gasstream containing'entrained particles of the cleaning agent dissolved in the combustible solvent and to mix the gaseous fuel containing' the entrained cleaning agent in the combustible solvent in a mixing zone or chamber with oxygen, the latter also being under superatmospheric pressure from a cylinder or other storage container. The mixture is then burned by passing it through a suitable orifice or similar device and igniting it to produce a flame which is applied preferably continuously to a strip line of wire,

rods, tubes, flat sheets or coiled sheets. An apparatus suitable for this purpose is commercially available under the name Gasfluxer. In the operation of this apparatus the fuel gas is normally kept under a superatmospheric pressure not exceeding 15 pounds per square inch (psi) and the oxygen under superatmospheric pressure of not more than 20 psi.

It is preferable to preheat the metal to be exposed to the gas flame treatment to a temperature above the boiling point of water but below that at which any.

change in the physical characteristic of the metal occurs. For aluminum the preheat temperature is preferably 250 to 350F., for steel 350 to 600F. and for hot dip galvanized steel (zinc surfaced steel) 250 to 350F. In the event the metal is contaminated with oil it is preferable that the preheat be performed by a superheated steam jet under pressure to mobilize the oil and blast it off into a receiving receptacle.

The temperature of the metal during the flame treatment and the time of treatment for steel and steel alloys is usually within the range of 250 to 600F. for one to sixty seconds. for aluminum and aluminum alloys 100 to 350F. for one to sixty seconds. and for hot dip galvanized and zinc or zinc alloy coatings 100 to 350F. for l to 60 seconds.

The flame temperature can be higher for a thick metal than a thinner metal but a controlling factor is the temperature which the metal itself attains and this will depend upon not only the metal gauge but also the speed with which the metal moves past the flame or. in other words, the time of contact of the metal with the flame. On iron and steel it may not be necessary to take many precautions with respect to the temperature. but on aluminum the temperature of the metal should be below the annealing temperature and on zinc or zinc surfaced articles the temperature should be below the flow temperature of the Zinc.

The flame can be applied to both sides of a moving continuous wire. rod, tube, flat sheet or coiled sheet.

The flame treatment with a cleaning agent as previously described provides a metal surface which has good receptivity to protective coatings of various types. One type of Protective Coating is a chromate conversion coating. Another type of protective coating is a film-forming polymer as applied. for example. in the form of a paint. Examples of such polymers are polyvinyl chloride. melamine. acrylic resin paints. epoxy resin paints, mixed epoxy-acrylic resin paints, polyester resins and polyurethane resins. These organic protective coatings can be applied as primary coats and/or as finish coats. Various primer coats include. for example, Lily Varnish Primer Primer and l 1 PL PRIMER 12870. Among the finish coats which can be used are. for example. Acrylic JT41 1-3, Duracron Super 610 and Duracron Super 8l0. Especially good results are obtained by applying a chromate conversion type of coating followed by an organic filmforming type coating.

Before a protective coating is applied to the flame treated metal it is desirable to allow the metal to cool preferably to a temperature below the boiling point of water. Chromate conversion coatings are usually prepared as aqueous baths and are preferably applied to the flame treated metal at a temperature within the range of l-200F. A typical example of a chromate conversion coating bath has the following composition:

Ingredients Parts by Weight Chromic Acid lcrO l Sulfuric acid (H .SO l Hydrofluoric Acid (36-4052 Fluohoric Acid Zinc Oxide Water 4.000

Optionally 0.25 to 1 part of sodium orthosilicate is added to the foregoing chromate conversion bath to provide repellancy to fluids, to act as a glazing coating and to render the deposited film less pervious to water creepage.

The protective coating can be applied in many different ways, for example, by spraying or by rollers similar to the type of rollers used for the application of paints where the coating material is introduced into the inside of the roller.

Applicator rollers may be used on one or both sides of moving wire. rods. tubes, flat sheets and coiled sheets. The metal preferably should be kept heated during the application of the protective coating. This can be done in several ways. for example, by electrical inductive heating or by using electrically heated conductive rolls or by otherwise heating the rollers employed to apply the protective coating.

The invention is advantageous in making it possible to clean and coat metals of the type described with a minimum consumption of energy sources, a minimum usage of liquids and chemicals such as rinse water resulting in a minimum pollution of air, water and land, a minimum cost of equipment, a minimum cost of maintenance. a minimum skilled labor requirement. minimum instrumentation and control. increased linear speeds. greater uniformity of coatings, greater physical. chemical and corrosion resistance properties, reduction in production costs and flexibility for off and on time requirements over weekends and holidays.

For magnetic metals, electro-induction equipment couldbe used as a source of heat to complete the combustion of the applied chemical purging materials.

In some cases it may be desirable to rinse the flame cleaned metal with a high pressure water spray to remove loose adhering particles.

lf the protective coating which is to be applied to the flame cleaned metal contains no highly volatile solvents the metal can be cooled to temperatures appropriate to the characteristics of the coating material, e.g., 250F. to 400F. Thus, it is possible to produce baked coatings while taking advantage of the heat already present in the metal due to the flame cleaning.

The invention is hereby claimed as follows:

1. A process of cleaning a metal in the form of wires, rods, tubes. flat sheets and coiled sheets. which comprises bringing said metal into contact with a flame produced by the combustion of a gaseous fuel under superatmospheric pressure in the presence of a metal cleaning agent dissolved in a combustible liquid solvent at controlled temperatures and for periods of time and under conditions sufficient to cause combustion of said solvent and to clean said metal simultaneously with the combustion of the solvent and provide a surface adapted to receive a protective coating, without destroying the physical properties of the metal, and thereafter removing said metal from said flame.

2. A process as claimed in claim 1 in which said cleaning agent dissolved in a combustible solvent is a saturated solution of boric acid in methanol.

3. A process as claimed in claim 1 in which said metal is preheated to a temperature of at least 250F. prior to bringing it into contact with said flame.

4. A process as claimed in claim 1 in which a protective coating is applied to said metal after said metal is cleaned and removed from the flame.

5. A process as claimed in claim 4 in which said pro- 

1. A PROCESS OF CLEANING A METAL IN THE FORM OF WIRES, RODS, TUBES, FLAT SHEETS AND COILED SHEETS, WHICH COMPRISES BRINGING SAID METAL INTO CONTACT WITH A FLAME PRODUCED BY THE COMBUSTION OF A GASEOUS FUEL UNDER SUPERATMOSPHERIC PRESSURE IN THE PRESENCE OF A METAL CLEANING AGENT DISSOLVED IN A COMBUSTIBLE LIQUID SOLVENT AT CONTROLLED TEMPERATURES AND FOR PERIODS OF TIME AND UNDER CONDITIONS SUFFICIENT TO CAUSE COMBUSTION OF SAID SOLVENT AND TO CLEAN SAID METAL SIMULTANEOUSLY WITH THE COMBUSTION OF THE SOLVENT AND PROVIDE A SURFACE ADAPTED TO RECEIVE A PROTECTIVE COATING, WITHOOUT DESTROYING THE PHYSICAL PROPERTIES OF THE METAL, AND THEREAFTER REMOVING SAID METAL FROM SAID FLAME.
 2. A process as claimed in claim 1 in which said cleaning agent dissolved in a combustible solvent is a saturated solution of boric acid in methanol.
 3. A process as claimed in claim 1 in which said metal is preheated to a temperature of at least 250*F. prior to bringing it into contact with said flame.
 4. A process as claimed in claim 1 in which a protective coating is applied to said metal after said metal is cleaned and removed from the flame.
 5. A process as claimed in claim 4 in which said protective coating is an organic film-forming coating.
 6. A process as claimed in claim 1 in which said metal is selected from the group consisting of steel and steel alloys, aluminum and aluminum alloys, zinc surfaced steel and zinc alloys. 